Application of Spectral Proper Orthogonal Decomposition (SPOD) on a Broad Spectrum Statistically Stationary Flowfield*

Although overshadowed by its space-only counterpart, Spectral Proper Orthogonal Decomposition (SPOD) was incepted many decades ago and can be considered the frequency domain form of Proper Orthogonal Decomposition (POD). Recent work shows that SPOD can reduce flow fields into structures that evolve coherently in time and space. Because of this characteristic, SPOD is a method well suited for statistically stationary flows, data that are random about a mean and do not grow or decay in time. In this work SPOD is applied to a flow field extracted from the surface of a rocket body in transonic flight. All aerodynamic vehicles experience broad spectrum loading in the transonic regime; this is known as "buffet". SPOD is a step in identifying the physics responsible for buffet. Specifically, the extraction of flow features at high energy frequencies within the broad spectrum can be very helpful for reduced order model construction or tool development for flow driven structural analysis. Future applications will push this study even further with the implementation of SPOD on a three-dimensional rotorcraft wake.